Video encoding and decoding methods and device using same

ABSTRACT

The present invention relates to video encoding/decoding methods and device, wherein the video encoding method according to the invention comprises the following steps: acquiring information of peripheral blocks; setting the information about a current block based on the information of the peripheral blocks; and encoding the current block based on the set information, wherein the current block and the peripheral blocks may be a CU (coding unit).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/060,051filed on Mar. 3, 2016, which is a continuation of application Ser. No.14/130,071 having a 371(c) date of Dec. 30, 2013, which is a U.S.national stage application of International Application No.PCT/KR2012/005251 filed on Jul. 2, 2012, which claims the benefit ofKorean Patent Application No. 10-201.1-0065431 filed on Jul. 1, 2011,Korean Patent Application No. 10-2011-0082462, filed on Aug. 18, 2011,and Korean Patent Application No. 10-2012-0071620, filed on Jul. 2,2012, in the Korean Intellectual Property Office, the entire disclosuresof which are incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates to a video encoding/decoding technology,and more particularly, to a method and apparatus for encoding/decoding acurrent coding unit (CU) using surrounding CUs.

BACKGROUND ART

With the recent establishment of multimedia environment, variousterminals and networks have been used and user demands have beendiversified.

For example, as the performance and computing ability of a terminal arediversified, the terminal supports various performances. Furthermore,networks for transmitting information are also diversified according toexternal structures such as wired and wireless networks, types oftransmitted information, information quantity, speed, etc. A userselects a terminal and a network according to a desired function, andthe spectrum of terminals and networks, provided by companies to users,is extended.

As a high definition (HD) broadcast service is extended not onlydomestically but also globally, many users become accustomed to videoshaving high resolution and high definition. Accordingly, video servicerelated organizations accelerate development of next-generation videoapparatuses.

Furthermore, an increasing attention to ultra high definition (UHD) morethan four times HD requires a compression technique for video havinghigher resolution and higher picture quality.

To compress and process video, inter prediction for predicting pixelvalues included in a current picture from a picture temporally beforeand/or after the current picture, intra prediction for predicting thepixel values included in the current picture using information on pixelsin the current picture, entropy coding for allocating a short code to asymbol of high frequency and allocating a long code to a symbol of lowfrequency, etc. can be used.

As demands for HD video service increase, a method of using informationof neighboring blocks is needed to appropriately control or minimize thequantity of transmitted information or the quantity of processedinformation.

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a method and apparatusfor encoding/decoding a current largest coding unit (LCU) usinginformation of neighboring LCUs.

Another object of the present invention is to provide a method andapparatus for encoding/decoding a higher layer of the current LCU usingcoding information of a lower layer or cost. In the case of encodingusing inter prediction, the present invention can limit the number ofreference picture candidates of prediction units (PUs) belonging to aupper depth CU using encoding cost of a lower depth CU.

Technical Solution

According to one aspect of the present invention, a video encodingmethod includes obtaining information about neighboring blocks,configuring information about a current block on the basis of theinformation about the neighboring blocks, and encoding the current blockon the basis of the configured information, wherein the current blockand the neighboring blocks are coding units (CUs).

When the current block is a current largest coding unit (LCU)corresponding a coding target and the neighboring blocks are neighboringLCUs of the current LCU, in the configuring of the information about thecurrent block, information to be used as information about the currentLCU may be selected from coding information about the neighboring LCUs.The coding information may be a maximum coding depth, and in theconfiguring of the information about the current block, a maximum codingdepth of the current LCU may be set on the basis of the largest value ofmaximum coding depths of the neighboring LCUs.

When the current block is a upper depth CU and the neighboring blocksare lower depth CUs, in the configuring of the information about thecurrent block, reference pictures of the lower depth CUs may be set asreference pictures of the upper depth CU when a prediction direction ofthe lower depth CUs corresponds to a prediction direction of the upperdepth CU.

When the current block is a higher depth CU and the neighboring blocksare lower depth CUs, in the configuring of the information about thecurrent block, motion information about the current block may be derivedusing motion information about a neighboring block having a partitionsize and a partition position corresponding to the current block, fromamong the neighboring blocks.

According to another aspect of the present invention, a video decodingmethod includes obtaining information about neighboring blocks, derivinginformation about a current block on the basis of the information aboutthe neighboring blocks, and decoding the current block on the basis ofthe configured information, wherein the current block and theneighboring blocks are CUs.

When the current block is a current LCU corresponding a coding targetand the neighboring blocks are neighboring LCUs of the current LCU, inthe deriving of the information about the current block, information tobe used as information about the current LCU may be selected from codinginformation about the neighboring LCUs. The coding information may be amaximum coding depth and, in the deriving of the information about thecurrent block, a maximum coding depth of the current LCU may be derivedon the basis of the largest value of maximum coding depths of theneighboring LCUs.

When the current block is a higher depth CU and the neighboring blocksare lower depth CUs, in the deriving of the information about thecurrent block, reference pictures of the lower depth CUs may be used asreference pictures of the higher depth CU when a prediction direction ofthe lower depth CUs corresponds to a prediction direction of the upperdepth CU.

When the current block is a upper depth CU and the neighboring blocksare lower depth CUs, in the deriving of the information about thecurrent block, motion information about the current block may be derivedusing motion information about a neighboring block having a partitionsize and a partition position corresponding to the current block, fromamong the neighboring blocks.

According to another aspect of the present invention, a video encoderincludes a predictor for predicting information about a current block, aquantizer for quantizing the predicted information, and an entropyencoding unit for entropy-encoding the quantized information, whereinthe predictor predicts the current block on the basis of informationabout neighboring blocks of the current block, and the current block andthe neighboring blocks are CUs.

According to another aspect of the present invention, a video decoderincludes a entropy decoding unit for entropy-decoding a received bitstream, a dequantizer for inversely quantizing the entropy-decodedinformation, and a predictor for predicting a current block on the basisof the inversely quantized information, wherein the predictor predictsthe current block on the basis of information about neighboring blocksof the current block, and the current block and the neighboring blocksare CUs.

Advantageous Effects

The present invention can encode/decode the current LCU usinginformation about neighboring LCUs so as to reduce complexity andincrease coding efficiency.

In addition, the present invention can decrease complexity and increasecoding efficiency by using coding information or cost of a lower layerwhen a higher layer of the current LCU is encoded/decoded.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an encoderaccording to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a configuration of a decoderaccording to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating an encoding/decoding method accordingto an embodiment of the present invention;

FIG. 4 illustrates a method for deriving coding information of a currentLCU from coding information of neighboring LCUs according to anembodiment of the present invention;

FIG. 5 illustrates a method for encoding/decoding a upper depth CU usingcoding information of a lower depth CU according to an embodiment of thepresent invention;

FIG. 6 illustrates an example of splitting a LCU;

FIG. 7 is a flowchart illustrating an encoding/decoding method accordingto another embodiment of the present invention;

FIG. 8 is a flowchart illustrating a method for limiting referencepictures of a upper depth CU using coding information of a lower depthCU when the upper depth CU is encoded/decoded according to the presentinvention; and

FIG. 9 illustrates a method of using a correspondence relationshipbetween a upper depth CU and a lower depth CU when prediction isperformed according to the present invention.

MODE FOR INVENTION

The above and other aspects of the present invention will be describedin detail through preferred embodiments with reference to theaccompanying drawings. In the following description of the presentinvention, a detailed description of known functions and configurationsincorporated herein will be omitted when it may obscure the subjectmatter of the present invention.

FIG. 1 is a block diagram illustrating a configuration of an encoderaccording to an embodiment of the present invention.

Referring to FIG. 1, the encoder 100 includes an inter predictor 110, anintra predictor 120, a switch 125, a subtractor 130, a transformer 135,a quantizer 140, an entropy encoding module 150, a dequantizer 160, aninverse transformer 170, an adder 175, a filter 180, and a picturebuffer 190.

The encoder 100 may encode an input video in an intra mode or an intermode and output a bit stream. The switch 125 is switched to the intramode in the intra mode and switched to the inter mode in the inter mode.The encoder 100 may generate a prediction block for an input block ofthe input video, and then encode a difference between the input blockand the prediction block.

In the intra mode, the intra predictor 120 may generate the predictionblock by performing spatial prediction using pixel values of previouslycoded blocks adjacent to a current block.

In the inter mode, the inter predictor 120 may obtain a motion vector bydetecting a region corresponding to the input block from referencepictures stored in the picture buffer 190 in a motion estimationprocedure. The inter predictor 110 may generate the prediction block byperforming motion compensation using the motion vector and the referencepictures stored in the picture buffer 190.

The subtractor 130 may generate a residual block using a differencebetween the input block and the generated prediction block. Thetransformer 135 may transform the residual block to output a transformcoefficient. The quantizer 140 may quantize the transform coefficientinput thereto according to a quantization parameter to output aquantized coefficient. The entropy encoding module 150 mayentropy-encode the quantized coefficient according to probabilitydistribution on the basis of values generated by the quantizer 140 orencoding parameters generated during an encoding process to output thebit stream.

The quantized coefficient may be inversely quantized by the dequantizer160 and inversely transformed by the inverse transformer 170. Theinversely quantized and inversely transformed coefficient may be addedto the prediction block by the adder 175 to generate a reconstructedblock.

The reconstructed block passes through the filter 180. The filter 180may apply at least one of a deblocking filter, a sample adaptive offset(SAO), and an adaptive loop filter (ALF) to the reconstructed block or areconstructed picture. The reconstructed block output from the filter180 may be stored in the picture buffer 190.

FIG. 2 is a block diagram illustrating a configuration of a decoderaccording to an embodiment of the present invention.

Referring to FIG. 2, the decoder 200 may include an entropy decodingmodule 210, a dequantizer 220, an inverse transformer 230, an intrapredictor 240, an inter predictor 250, a filter 260, a picture buffer270.

The decoder 200 may receive a bit stream output from an encoder anddecode the bit stream in the intra mode or inter mode to output areconfigured picture, that is, a reconstructed picture. A switchincluded in the decoder 200 is switched to the intra mode in the intramode and switched to the inter mode in the inter mode.

The decoder 200 may obtain a reconstructed residual block from thereceived bit stream, generate a prediction block and sum thereconstructed residual block and the prediction block to generate areconfigured block, that is, a reconstructed block.

The entropy decoding module 210 may entropy-decode the input bit streamaccording to probability distribution. Through entropy decoding, aquantized (transform) coefficient may be generated.

The quantized coefficient may be inversely quantized by the dequantizer220 and inversely transformed by the inverse transformer 230, and thus areconstructed residual block may be generated.

In the intra mode, the intra predictor 240 may generate a predictionblock by performing spatial prediction using pixel values of previouslydecoded blocks around a current block. In the inter mode, the interpredictor 250 may generate the prediction block by performing motioncompensation using a motion vector and reference pictures stored in thepicture buffer 270.

The reconstructed residual block and the prediction block are summed bythe adder 255. The summed block passes through the filter 260. Thefilter 260 may apply at least one of a deblocking filter, an SAO and anALF to the reconstructed block or a reconstructed picture. The filter260 may determine whether to use the ALF when the SAO is applied to thereconstructed block. The filter 260 outputs the reconfigured picture,that is, reconstructed picture. The reconstructed picture may be storedin the picture buffer 270 and used for inter prediction.

A coding unit (CU), which is a hierarchical coding unit, is definedwithout using a macroblock having a fixed size, and encoding/decodingcan be performed by variably setting the size of the CU.

It is possible to define the largest CU (LCU) and the smallest CU (SCU).For example, the LCU can be defined to have a size of 64×64 pixels andthe SCU can be defined to have a size of 8×8 pixels. An image may behierarchically encoded by defining CUs having various sizes between theLCU and the SCU.

Here, CUs of various sizes have depth information. If the depth of theLCU is 0 and the depth of the SCU is D, CUs having sizes between the LCUand the SCU have depths in the range of 0 to D.

An encoded bit stream may include split_coding_unit_flag for a CU ofeach size as information for signaling the CU size. Thesplit_coding_unit_flag is information indicating whether a current CU issplit into CUs of a smaller size, that is, CUs having a upper depth.Here, the current CU is a CU to be encoded or decoded.

In an encoding method according to an embodiment of the presentinvention, a current LCU may be encoded using coding information aboutneighboring LCUs. For example, a maximum coding depth of the current LCUcan be predicted using maximum depth information of neighboring LCUs.Here, the current LCU is an LCU to be encoded or decoded.

In the current LCU, a higher layer CU may be encoded using informationof a lower layer. Here, a lower layer represents an encoding/decodingtarget (e.g. CU, PU, pixel, etc.) having a lower depth whereas a higherlayer represents an encoding/decoding target (e.g. CU, PU, pixel, etc.)having a upper depth.

In the specification, when the depth of the LCU is 0 and the depth ofthe SCU is D, as described above, a depth closer to the LCU is referredto as a lower depth and a depth closer to the SCU is referred to as aupper depth. For example, depth d is lower than depth d+1 (0<d<D). Incoding using inter prediction, the number of reference picturecandidates for a prediction unit (PU) belonging to a higher CU can belimited using coding information of a lower depth CU.

Since a CU may have various sizes and has a hierarchical codingstructure, complexity of coding the CU increases while coding efficiencyis high. For example, an encoder calculates costs of coding methodsapplicable to CUs of available sizes to determine an optimized CU sizeand coding method. In this case, high calculation complexity is requiredbecause it is necessary to consider all coding methods applicable to allavailable CU sizes.

Here, it is possible to reduce calculation complexity and increasecoding efficiency by removing redundancy of the current LCU andneighboring LCUs. A method of using information about neighboring LCUsfor the current LCU can be considered to be a method for removingredundancy of the current LCU and the neighboring LCUs.

Furthermore, redundancy in the current LCU can be removed to reducecomplexity and increase coding efficiency by using information about alower layer (lower depth) in the current LCU.

A description will be given of an encoding/decoding method according toan embodiment with reference to the detached drawings.

FIG. 3 is a flowchart illustrating an encoding/decoding method accordingto an embodiment of the present invention. FIG. 3 illustrates a methodfor encoding/decoding the current LCU using coding information ofneighboring LCUs.

While the method illustrated in FIG. 3 may be performed in theindividual modules included in the encoder and the decoder shown inFIGS. 1 and 2, the encoder and the decoder carry out operations of themodules in the following description for convenience of explanation.

Referring to FIG. 3, the encoder/decoder specifies locations of theneighboring LCUs of the current LCU (S310). For example, if the numberof available LCUs located adjacent to the current LCU is n, theencoder/decoder obtains coordinates of the n neighboring LCUs. Thecoordinates specifying the locations of the neighboring LCUs maycorrespond to positions (x, y) of left-above pixels of the LCUs.

The encoder/decoder obtains coding information of the neighboring LCUs(S320). The encoder/decoder obtains coding information of the nneighboring LCUs specified in step S310. Here, the obtained codinginformation includes information about CU segmentation(split_coding_unit_flag), an LCU maximum depth (LCU_max_depth), an LCUspilt map (LCU_split_map), an LCU prediction type (LCU_Pred_Type), andan LCU partition size (LCU_Part_Size).

The LCU prediction type is information indicating whether an appliedprediction type corresponds to inter prediction or intra prediction. TheLCU prediction type may be information indicating which one of a skipmode, a merge mode and a method using MVP is used when inter predictionmode is applied and may be information indicating an intra predictionmode when intra prediction is applied. For example, the LCU predictiontype may include skip_flag indicating application of the skip mode,ref_idx indicating a reference picture index, inter_pred_idc indicatingan inter prediction method, mvp_idx indicating a motion vectorpredictor, merge_flag indicating whether the merge mode is applied,merge_idx indicating a merge target, prev_intra_luma_pred_flagindicating estimation of an intra prediction mode of a luma componentfrom an intra prediction mode of a neighboring block, mpm_idx indicatinga most frequently generated intra mode, intra_mode indicating an intraprediction mode, etc.

The LCU partition size is information representing an LCU partition formand may indicate whether LCU partition corresponds to 2N×2N, 2N×N orN×2N (N is the number of predetermined pixels).

The encoder/decoder encodes/decodes the current LCU on the basis of thecoding information obtained from the neighboring LCUs (S330).

For example, the encoder/decoder can predict a maximum depth of thecurrent LCU using depth information of the neighboring LCUs.

An LCU size may be fixed in a predetermined range. For example, an LCUcan have sizes corresponding to 8×8 pixels, 16×16 pixels, 32×32 pixelsand 64×64 pixels in the range of 8×8 pixels to 64×64 pixels.Furthermore, an LCU size may be variably determined such that it can bedefined in a wider range. For example, an LCU size can be defined tocorrespond to 8×8 pixels, 16×16 pixels, 32×32 pixels, 64×64 pixels and128×128 pixels in the range of 8×8 pixels to 128×128 pixels.

An LCU size and an SCU size used for encoding may be determined in theencoder and signaled to the decoder. For example, the SCU size can besignaled as log 2_min_coding_block_size_minus3. The LCU size can besignaled as a difference between the LCU size and the SCU size, such aslog 2_diff_max_min_coding_block_size. When the difference between theLCU size and the SCU size is signaled to the decoder, the decoder mayderive the LCU size using the received SCU size. The LCU size and theSCU size can be signaled through a sequence parameter set (SPS) by whichcoding information of a corresponding sequence is transmitted.

FIG. 4 illustrates a method for deriving coding information of thecurrent LCU from coding information of neighboring LCUs according to anembodiment of the present invention.

FIG. 4 shows a case in which four LCUs A_LCU, B_LCU, C_LCU and D_LCU410, 420, 430 and 440 are located around the current LCU 400.

According to the present invention, the maximum coding depth of thecurrent LCU can be predicted using maximum depth information of LCUsA_LCU, B_LCU, C_LCU and D_LCU 410, 420, 430 and 440.

Equation 1 represents an exemplary method of predicting the maximumcoding depth of the current LCU using the neighboring LCUs A_LCU, B_LCU,C_LCU and D_LCU according to the present invention.

D=min(3,max(A_max_depth,B_max_depth,C_max_depth,D_max_depth)+X)  <Equation1>

In Equation 1, D denotes a maximum depth used for coding of the currentLCU, X is information about the difference between the LCU size and theSCU size and corresponds to log 2_diff_max_min_coding_block_size-1.

A_max_depth, B_max_depth, C_max_depth and D_max_depth respectivelyrepresent maximum depths of A_LCU, B_LCU, C_LCU and D_LCU.

For convenience of description, it is assumed that the LCU sizecorresponds to 64×64 pixels, the SCU size corresponds to 8×8 pixels,prediction of N×N pixels is performed for the SCU only in interprediction or intra prediction.

The encoder can determine an optimized CU size by performing ratedistortion optimization (RDO) on CUs of sizes corresponding to depth 0(64×64 pixels) to depth 3 (8×8 pixels).

Since the LCU size is 64×64 pixels and the SCU size is 8×8 pixels, asdescribed above, a maximum depth max_depth of an LCU corresponds to adepth of a CU (SCU) having a size of 8×8 pixels, that is, depth 3.

Here, a maximum depth applicable to coding of the current LCU can bedetermined separately from the depth of the SCU. If the maximum depthapplicable to coding of the current LCU is D, D can be determined asrepresented by Equation 2.

D=min(3,max(A_max_depth,B_max_depth,C_max_depth,D_max_depth)+2)  <Equation2>

When the depths of the four neighboring LCUs A_LCU, B_LCU, C_LCU andD_LCU are all 0, that is, when all the four neighboring LCUs are encodedto 64×64 pixels without being split, the maximum depth max_cu_depth ofthe current LCU, D, becomes 2 according to Equation 2. Accordingly, theencoder performs RDO on only CUs having sizes of 64×64 pixels, 32×32pixels and 16×16 pixels and does not carry out RDO on a CU (SCU) havinga size of 8×8 pixels.

While it is assumed that prediction of N×N pixels is performed on theSCU only, prediction of N×N pixels may be performed on only the smallestblock to which RDO is applied. For example, when the maximum depth ofthe current LCU is 2 as described above, RDO is not performed on the CUhaving a size of 8×8 pixels although the SCU corresponds to the CUhaving a size of 8×8 pixels, and thus prediction of N×N pixels can becarried out on a block of a size corresponding to 16×16 pixels.

Alternatively, as an example of deriving the coding information of thecurrent LCU using the coding information of the neighboring LCU, thereis a method of deriving/estimating split information on the current LCUusing split information on the neighboring LCU.

For example, the encoder/decoder can derive/estimate asplit_coding_unit_flag value for the current LCU on the basis of asplit_coding_unit_flag value corresponding to the split informationabout the neighboring LCUs. Here, when the split_coding_unit_flag valueis 0, this indicates that a CU is not split any more. If thesplit_coding_unit_flag value is 1, this indicates that the CU is splitinto four sub CUs.

Referring to FIG. 4, the encoder/decoder may check split informationsplit_coding_unit_flag about the neighboring LCUs A_LCU, B_LCU, C_LCUand D_LCU 410, 420, 430 and 440 before encoding/decoding the current LCU400.

The encoder/decoder may set the split_coding_unit_flag value of thecurrent LCU to 0 if all the checked split_coding_unit_flag values of thefour neighboring LCUs are 0. Since the split_coding_unit_flag for thecurrent LCU is not transmitted and can be derived from the neighboringLCUs, 1 bit used for transmission of the split_coding_unit_flag of thecurrent LCU can be reduced. Furthermore, since thesplit_coding_unit_flag value of the current LCU is set to 0, complexitycan be reduced unless a CU smaller than the current LCU is encoded.

The encoder/decoder can set the split_coding_unit_flag value of thecurrent LCU to 1 if at least one of the checked split_coding_unit_flagvalues of the fourth neighboring LCUs is 1. Even in this case, thesplit_coding_unit_flag for the current LCU is not transmitted and can bederived from the neighboring LCUs, and thus 1 bit used for transmissionof the split_coding_unit_flag of the current LCU can be reduced. Inaddition, since the split_coding_unit_flag value of the current LCU isset to 1, complexity can be reduced if only split CUs having a smallsize are encoded except the current LCU.

Consequently, split information split_coding_unit_flag may not betransmitted for each LCU at depth 0.

Table 1 shows an exemplary syntax when split information about thecurrent LCU is derived using split information about neighboring LCUs.

TABLE 1 Descriptor coding_tree( x0, y0, log2CUSize ) { if( x0 + ( 1 <<1og2CUSize ) <= PicWidthInSamples_(L) && y0 + ( 1 << log2CUSize ) <=PicHeightInSamples_(L) &&) if( !entropy_coding_mode_flag && slice_type!= I ) cu_split_pred_part_mode[ x0 ][ y0 ] ce(v)  else if(log2CUSize!=>Log2MaxCUSize && log2CUSize > Log2MinCUSize ) split_coding_unit_flag[ x0][ y0 ] u(1) | ae(v) if( adaptive_loop_filter_flag &&alf_cu_control_flag ) { cuDepth = Log2MaxCUSize − log2CUSize if( cuDepth<= alf_cu_control_max_depth ) if( cuDepth == alf_cu_control_max_depth ∥split_coding_unit_flag[ x0 ][ y0 ] == 0 ) AlfCuFlagIdx++ }

Table 1 shows a case in which an entropy encoding mode corresponds tocontext-based adaptive binary arithmetic coding (CABAC).

Referring to Table 1, the syntax of the current LCU can be adaptivelyentropy-coded according to coding information of the neighboring LCUs.

For example, if CABAC is used as an entropy coding method as shown inTable 1, a context index delta value of the syntax of the current LCUcan be set based on syntax counting of the neighboring LCU.

Here, the context index depth value can be set according to Equation 3.

Context index=offset+increment+delta  <Equation 3>

Examples of a context that can be set for the current LCU using Equation3 include a merge index merge_idx, a motion vector predictor indexmvp_idx, a remaining prediction mode rem_intra_luma_pred_mod except mostprobable mode (MPM) in the intra prediction mode, etc.

If the neighboring LCUs are encoded to an LCU size instead of beingsplit, a most probable symbol (MPS) value may be set to 0 when splitinformation split_coding_unit_flag about a CU having a depth lower thanthe maximum depth by 1, max_cu_depth-1, is encoded.

When context based adaptive variable length coding (CAVLC) is used as anentropy coding method, distinguished from Table 1, syntax counting ofthe neighboring LCUs may be reflected in an adaptive sorting table ofthe current LCU or used to select a variable length code table. That is,probability of the neighboring LCU syntax can be reflected inencoding/decoding of the current LCU using correlation between thecoding information of the current LCU and the coding information of theneighboring LCUs.

For example, if the neighboring LCUs are encoded to an LCU size insteadof being mode-split, a table that defines the split information aboutthe CU having a depth lower than the maximum depth by 1, max_cu_depth-1,and prediction mode information can be modified from Table 2 to Table 3and used.

TABLE 2 cu_split_pred_part_mode split_coding_ unit_flag merge_flagPredMode PartMode 0 1 — — — 1 0 — MODE_SKIP PART_2Nx2N 2 0 1 MODE_INTERPART_2Nx2N 3 0 0 MODE_INTER PART_2Nx2N 4 0 — MODE_INTER PART_2NxN 5 0 —MODE_INTER PART_Nx2N 6 0 — MODE_INTRA PART_2Nx2N

TABLE 3 cu_split_pred_part_mode split_coding_unit_flag merge_flagPredMode PartMode 0 0 — MODE_SKIP PART_2Nx2N 1 0 1 MODE_INTER PART_2Nx2N2 0 0 MODE_INTER PART_2Nx2N 3 0 — MODE_INTER PART_2NxN 4 0 — MODE_INTERPART_Nx2N 5 0 — MODE_INTRA PART_2Nx2N 6 1 — — —

Referring to Table 2 and Table 3, when the split_coding_unit_flag valueis 1, cu_split_pred_part_mode that indicates partition and predictionmodes may be adaptively allocated according to probabilities ofgeneration of other modes.

In addition to the above-mentioned method for encoding/decoding thecurrent LCU using information of neighboring LCUs, a method forencoding/decoding a upper depth CU using coding information of a lowerdepth CU of the current LCU can be considered as a method forencoding/decoding a current block using information about neighboringblocks.

FIG. 5 illustrates a method for encoding/decoding a upper depth CU usingcoding information of a lower depth CU according to an embodiment of thepresent invention.

Referring to FIG. 5, when a lower depth CU 510 is split into four upperdepth CUs 520, 530, 540 and 550, the upper depth CUs 520, 530, 540 and550 can be encoded/decoded using coding information of the lower depthCU 510.

FIG. 6 illustrates an example of splitting a LCU.

Referring to FIG. 6, an LCU 610 having a size of 64×64 pixels may besplit into CUs of various sizes and encoded.

When the LCU is split into CUs of various sizes, while coding efficiencyincreases because encoding can be performed on each CU having anoptimized size, complexity also increases. Specifically, the encoderdetermines optimized CU sizes and a PU coding mode for each CU size. Toachieve this, the encoder needs to calculate rate-distortion cost foreach coding mode applicable to each CU size, and thus high complexity isrequired. In this case, complexity can be considerably reduced usingcorrelation between coding information of a lower depth CU and codinginformation of a upper depth CU, as described above.

FIG. 7 is a flowchart illustrating an encoding/decoding method accordingto another embodiment of the present invention. FIG. 7 illustrates amethod for encoding/decoding a higher layer of the current LCU usingcoding information of a lower layer.

While the method illustrated in FIG. 7 may be performed in theindividual modules included in the encoder and the decoder shown inFIGS. 1 and 2, the encoder and the decoder carry out operations of themodules in the following description for convenience of explanation.

Referring to FIG. 7, the encoder/decoder obtains coding informationabout a lower depth CU of the current LCU (S710). When theencoder/decoder encodes/decodes a CU having a predetermined depth, theencoder/decoder can check and obtain coding information of an availablelower depth CU.

Here, the obtained coding information includes information about splitof the CU (split_coding_unit_flag), an LCU maximum depth(LCU_max_depth), an LCU split map (LCU_split_map), an LCU predictiontype (LCU_Pred_Type), and an LCU partition size (LCU_Part_Size).

The LCU prediction type is information indicating whether an appliedprediction type corresponds to inter prediction or intra prediction. TheLCU prediction type may be information indicating which one of a skipmode, a merge mode and a method using MVP is used when inter predictionmode is applied and may be information indicating an intra predictionmode when intra prediction is applied. For example, the LCU predictiontype may include skip_flag indicating application of the skip mode,ref_idx indicating a reference picture index, inter_pred_idc indicatingan inter prediction method, mvp_idx indicating a motion vectorpredictor, merge_flag indicating whether the merge mode is applied,merge_idx indicating a merge target, prev_intra_luma_pred_flagindicating estimation of an intra prediction mode of a luma componentfrom an intra prediction mode of a neighboring block, mpm_idx indicatinga most frequently generated intra_mode, intra_mode indicating an intraprediction mode, etc.

The LCU partition size is information representing an LCU partition formand may indicate whether LCU partition corresponds to 2N×2N, 2N×N orN×2N (N is the number of predetermined pixels).

The encoder/decoder predicts coding information of the upper depth CU onthe basis of the obtained coding information of the lower depth CU(S720). For example, if a PU belonging to the upper depth CU isinter-predicted, reference picture information and/or a motion vector ofthe PU belonging to the upper depth CU can be predicted from the codinginformation of the lower depth CU.

The encoder/decoder can encode/decode the upper depth CU on the basis ofthe predicted coding information (S730).

The encoder/decoder may predict the coding information of the upperdepth CU using the coding information of the lower depth CU. Forexample, the encoder/decoder can limit reference pictures used forprediction of a PU included in the upper depth CU to a specific rangewhen encoding/decoding the upper depth CU using the coding informationof the lower depth CU. It is possible to increase compression efficiencywhile reducing complexity by limiting used reference pictures topredetermined reference pictures.

FIG. 8 is a flowchart illustrating a method for limiting referencepictures of a upper depth CU using coding information of a lower depthCU when the upper depth CU is encoded/decoded according to the presentinvention.

While the method illustrated in FIG. 8 may be performed by apredetermined module (e.g. inter predictor) included in theencoder/decoder shown in FIGS. 1 and 2, the encoder or the decoder(referred to as encoder/decoder) performs the method in the followingdescription for convenience of explanation.

Referring to FIG. 8, the encoder/decoder obtains information about thelower depth CU (S800). For example, the encoder/decoder obtainsinformation indicating whether the lower depth CU is inter-predicted orintra-predicted. Furthermore, the encoder/decoder may obtain informationrepresenting which one of a skip mode, a merge mode and MVP is used ifthe lower depth CU is inter-predicted and obtain information about anintra prediction mode if the lower depth CU is intra-predicted.

The encoder may signal the obtained information to the decoder, and thedecoder may obtain the information by parsing a bit stream received fromthe encoder.

The encoder/decoder determines whether the lower depth CU isinter-predicted on the basis of the obtained information (S805).

If the lower depth CU is not inter-predicted (when the lower depth CU isintra-predicted), the encoder/decoder may inter-predict the upper depthCU which is the current block using all reference pictures for the upperdepth CU in L0 and L1 predictions (S810). If the lower depth CU isinter-predicted, the encoder/decoder may determine whether the skip modeor the merge mode is applied to the lower depth CU (S820).

The encoder/decoder may check information such as a merge index when theskip mode or the merge mode is applied to the lower depth CU (S825). Themerge index indicates motion information of a block, which is used asmotion information of the current block when the skip mode or the mergemode is applied.

The encoder/decoder determines whether the lower depth CU isL0-predicted, L1-predicted, or bi-predicted (S830). When a CU is in theinter mode, motion compensation may be performed on a block by blockbasis. Motion compensation is carried out by applying forward prediction(L0 prediction) and backward prediction (L1 prediction) to each block.Here, L0 is reference picture list 0 and L1 is reference picture list 1.

Prediction applied to a target block may be divided into a case in whichthe target block is encoded using only one of L0 prediction and L1prediction (uni-directional prediction) and a case in which the targetblock is encoded using both L0 prediction and L1 prediction(bi-prediction). A frame or a block that uses only one of L0 predictionand L1 prediction is referred to as a predictive frame (P frame) or a Pblock and a frame or a block that uses both L0 prediction and L1prediction is referred to as a bi-predictive frame (B frame) or a Bblock.

When bi-prediction is applied to the lower depth CU, the encoder/decoderchecks reference pictures of L0 and L1 (S835).

When L0 prediction is applied as uni-direction prediction to the lowerdepth CU, the encoder/decoder checks reference pictures of L0 (S840).

When L1 prediction is applied as uni-direction prediction to the lowerdepth CU, the encoder/decoder checks reference pictures of L1 (S845).

The encoder/decoder may restrict the reference pictures for the upperdepth CU on the basis of the information checked in steps S835, S840 andS845.

That is, when the prediction direction of the higher depth CUcorresponds to the prediction direction of the lower depth CU, it ispossible to perform inter prediction of the higher depth CU usingpictures corresponding to reference pictures of the lower depth CU fromamong reference picture candidates for the higher depth CU as referencepictures.

If the prediction direction of the upper depth CU is different from theprediction direction of the lower depth CU, it is possible to performinter prediction of the upper depth CU using all reference picturecandidates that belong to the prediction direction of the upper depthCU.

For example, if bi-prediction in L0 direction/L0 direction has beenapplied to the lower depth CU, a picture used as a reference picture forthe lower depth CU, from among the reference picture candidates for theupper depth CU, is used as a reference picture when L0 prediction isperformed on the upper depth CU which is a current block, whereas allthe reference picture candidates for the upper depth CU are used when L1prediction is performed on the upper depth CU (S850).

If bi-prediction in L0 direction/L1 direction has been applied to thelower depth CU, a picture used as a reference picture for L0 predictionof the lower depth CU, from among the reference picture candidates forthe upper depth CU corresponding to the current block, is used as areference picture when L0 prediction is performed on the upper depth CUwhich is a current block, whereas a picture used as a reference picturefor L1 prediction of the lower depth CU, from among the referencepicture candidates for the upper depth CU, is used as a referencepicture when L1 prediction is performed on the upper depth CU (S855).

If bi-prediction in L1 direction/L1 direction has been applied to thelower depth CU, all the reference picture candidates for the upper depthCU are used when L0 prediction is performed on the upper depth CU whichis a current block, whereas a picture used as a reference picture forthe lower depth CU is used as a reference picture when L1 prediction isperformed on the upper depth CU (S860).

If uni-directional prediction in L0 direction has been applied to thelower depth CU, a picture used as a reference picture for the lowerdepth CU, from among the reference picture candidates for the upperdepth CU, is used as a reference picture when L0 prediction is performedon the upper depth CU which is a current block, whereas all thereference picture candidates for the upper depth CU are used when L1prediction is performed on the upper depth CU (S865).

If uni-directional prediction in L1 direction has been applied to thelower depth CU, a picture used as a reference picture for the lowerdepth CU, from among the reference picture candidates for the upperdepth CU, is used when L1 prediction is performed on the upper depth CUwhich is a current block, whereas all the reference picture candidatesfor the upper depth CU are used when L0 prediction is performed on theupper depth CU (S870).

When the skip mode or the merge mode is applied to the lower depth CU,if the merge index for the lower depth CU is checked in step S825,prediction can be performed using a merge candidate or a skip candidateof the upper depth CU, which is indicated by the merge index for thelower depth CU, as a skip candidate or a merge candidate for the upperdepth CU in steps S850 to S870. Here, the skip candidate representsmotion information used as motion information of the current block or ablock having the motion information when the skip mode is applied. Themerge candidate represents motion information used as motion informationof the current block or a block having the motion information when themerge mode is applied.

Furthermore, when the skip mode or the merge mode is applied to thelower depth CU, prediction may be performed using the merge candidate orthe skip candidate of the upper depth CU, which is indicated by themerge index of the lower depth CU, as the skip candidate or the mergecandidate for the upper depth CU only when the prediction direction ofthe lower depth CU corresponds to the prediction direction of the upperdepth CU in steps S850 to S870 on the basis of the merge index of thelower depth CU, confirmed in step S825.

To check (obtain) the coding information of the lower depth CU and usemore correct information for the upper depth CU, it may be possible toperform prediction on a CU having an even-numbered depth (e.g. depth 0,depth 2) using only information on the corresponding depth in a normalmethod and to carry out prediction on a CU having an odd-numbered depth(e.g. depth 1, depth 3) using the coding information of the lower depthCU. That is, prediction of a CU of depth 1 can be performed using codinginformation about a CU of depth 0 and prediction of a CU of depth 3 canbe carried out using coding information about a CU of depth 2.

Accordingly, it is possible to reduce the influence of propagation,caused by application of the coding information about the CU of depth 0up to prediction of the CU of depth 3, and to increase predictionaccuracy when the coding information about the lower depth CU is usedfor all depths.

It may be possible to use motion information of the lower depth CUcorresponding to the upper depth CU when prediction of the upper depthCU is performed by checking a partition size or partition position ofthe lower depth CU.

FIG. 9 illustrates a method of using correspondence between a upperdepth CU and a lower depth CU when prediction is performed according tothe present invention. FIG. 9 shows a case in which a partition size anda partition position are used as correspondence between the upper depthCU and the lower depth CU.

Referring to FIG. 9, if a partition size of lower depth CUs 900 having adepth of n is 2N×N, CUs 945 and 950 from among upper depth CUs 940having a depth of n+1 may use motion information about a lower depth CU905 corresponding thereto as motion information thereof or may derivethe motion information thereof on the basis of the motion informationabout the lower depth CU 905. Otherwise, upper depth CUs 955 and 960 mayuse motion information about a lower depth CU 910 corresponding theretoas motion information thereof or may derive the motion informationthereof on the basis of the motion information about the lower depth CU910.

If a partition size of lower depth CUs 920 having a depth of n is N×2N,CUs 975 and 985 from among upper depth CUs 970 having a depth of n+1 mayuse motion information about a lower depth CU 925 corresponding theretoas motion information thereof or may derive the motion informationthereof on the basis of the motion information about the lower depth CU925. Otherwise, upper depth CUs 980 and 990 may use motion informationabout a lower depth CU 930 corresponding thereto as motion informationthereof or may derive the motion information thereof on the basis of themotion information about the lower depth CU 930.

While a CU has been described as the unit of encoding/decoding, this isexemplary and the present invention is not limited thereto. For example,descriptions of FIGS. 3 to 9 may be equally applied to a PU and a TUinstead of the CU.

Furthermore, while two embodiments (the embodiment of using codinginformation about neighboring LCUs, illustrated in FIGS. 3 and 4, andthe embodiment of using information about a lower depth block,illustrated in FIGS. 5 to 9) have been separately described, this is forthe purpose of clarifying description of the respective embodiments andthe present invention is not limited thereto. For example, the twoembodiments can be performed separately and carried out in a combinedmanner.

While the aforementioned exemplary methods have been described as stepsor blocks on the basis of flowcharts in the above-described exemplarysystem, the present invention is not limited to the order of steps andsome steps may be generated differently from the above steps orsimultaneously. Furthermore, the above-mentioned embodiments includevarious illustrations of various aspects. Accordingly, a combination ofthe embodiments should be understood as an embodiment of the presentinvention.

1. A method for decoding a video signal with a decoding apparatus, themethod comprising: determining, based on a merge flag obtained from thevideo signal, whether a merge mode is applied to a first predictionblock included in a coding block, the merge flag indicating whether themerge mode is applied to the first prediction block, the coding blockbeing partitioned to comprise a plurality of prediction blocks, thefirst prediction block being one of the prediction blocks; when themerge flag indicates that the merge mode is applied to the firstprediction block, determining a plurality of merge candidates of thefirst prediction block, wherein when the coding block has a pre-definedsize, the merge candidates are derived based on a position of the codingblock, and wherein when the coding block does not have the pre-definedsize, the merge candidates are derived based on a position of the firstprediction block; deriving motion information of the first predictionblock using the merge candidates; obtaining prediction samples of thefirst prediction block using the motion information; and obtainingreconstruction samples by using the prediction samples.
 2. The method ofclaim 1, wherein the merge candidates of the first prediction blockinclude at least one of neighboring blocks adjacent to the coding blockor the first prediction block, the neighboring blocks including a leftneighboring block, a top neighboring block, a top-right neighboringblock, a left-bottom neighboring block or a top-left neighboring block.3. The method of claim 1, wherein the pre-defined size is 8×8.
 4. Themethod of claim 1, wherein the first prediction block is a 2N×Nsub-block or a N×2N sub-block.